Fuel cell power plants use hydrogen as the fuel. Current technology includes conversion of hydrocarbon feeds to hydrogen by passing natural gas through a desulfurizer, a catalytic partial oxidizer (or other reformer), a water-gas shift reactor, and a preferential carbon monoxide oxidizer for the generation of significant hydrogen for use as a fuel in a fuel cell, in which hydrogen and oxygen on opposite sides of the electrolyte are converted to electricity and water, in the known fashion.
Referring to FIG. 1, hydrogen reformate is generated in a line 13 by a major reformer 14, such as a catalytic partial oxidizer (CPO), an auto-thermal reformer or a steam reformer, which in turn receives desulfurized hydrocarbon fuel, such as natural gas, over a line 16 from a hydrogen desulfurizer 17. The hydrogen desulfurizer 17 receives hydrocarbon fuel over a line 19. The CPO 14 also receives humidified air, from a suitable source such as an enthalpy recovery device, over a line 23. In the CPO 14, the hydrocarbons in the fuel react with the humidified air on a catalyst, such as rhodium, iridium or zirconia, to produce in the line 13 reformate which, for methane feedstock, is roughly 37% hydrogen, 14% CO, 4% CO2 and traces of other gases, which is further processed with water from a line 24 in a water-gas shift reactor 26 and a preferential CO oxidizer 27 to make it suitable for use as fuel in a line 31, such as for a fuel cell.
However, the hydrogen desulfurizer requires hydrogen enrichment in order to convert sulfur compounds, such as thiophene, into hydrogen sulfide, which is captured on adsorbents, such as zinc oxide. This hydrogen is provided by a hydrogen recycle blower 30 which pressurizes hydrogen from the line 31 and applies it over lines 32 and 33 to the hydrogen desulfurizer 17. A plurality of valves 34 allow adjustment of the processes, all as is known.
Problems with this system include the fact that the hydrogen blower 30 is expensive, and it consumes on the order of 2 kW of the power generated by the fuel cell for a 150 kW fuel cell power plant. Additionally, there is a significant amount of steam present in the hydrogen recycle stream 32 which has a negative impact on the hydrogen sulfide adsorption on zinc oxide in the hydrogen desulfurizer 17. This can impair the reduction of the level of sulfur, which must reach the parts-per-billion (pbb) level for fuel cell applications and to avoid rapid deactivation of catalysts used in the process.